A roller of the above-described type is disclosed, for example, in DE-GM No. 8214741. A rolling bearing is encompassed by a rolling body, the front side of which is closed by the bearing and the other side of which is provided with annular recesses. When this rolling body is to be injection-molded directly onto the outer ring of the bearing, an umbrella sprue is used because of the known satisfactory results of this method of injection molding. However, because the sprue is always directed axially, difficulties arise when the side faces of the bearing rings and the interposed bearing frame are without engagement. Furthermore, an annular sprue residue is formed on the side face of the inner wall portion, which must be removed in a subsequent process step if the side face must be flat due to operating conditions and, for example, flush with the outer ring.
A similar umbrella sprue is, for example, schematically depicted in FIG. 40 of Kunststoff-Taschenbuch by Sachtling, Issue 21, page 97. In the bore of the injection-molded workpiece a tool part must be inserted which at the same time forms the inner mold for the umbrella sprue by means of its conical side face. Likewise, when a hub or the like is to be injection-molded, finishing of the side face is necessary after shearing off of the umbrella sprue, in the case when the side face is to be utilized, for example, as an abutment face. This is also true for the radial vent shown in FIGS. 3-6 on page 19 of Maschinen-elemente aus thermoplastischen Kunststoffen, Grundlagen und Verbindungselemente by Erhard and Strickle. The umbrella sprue is formed on the side face of the inner wall portion. A tool is not shown in this figure.